The present invention relates to methods and apparatus for machining features such as flat surfaces onto work pieces, and more particularly, to methods and apparatus particularly useful in connection with machining such surfaces onto large quantities of relatively small, identical work pieces.
One prior method for machining, for example, longitudinally extending flat surfaces onto round work pieces such as screws requires a machine operator to manually insert the screws, one at a time, into a centerless grinder, and hold the screw against a guide while actuating the grinding wheel toward the screw to grind the flat. The screw is then removed and another screw is inserted, held, and ground by the operator. Such an operation, however, has several disadvantages. The operation is relatively slow since it requires the operator to take several steps for grinding each screw. The in-out plunging engagement between the grinding wheel and the work pieces causes the grinding wheel to break-down or wear at a relatively high rate, further reducing productivity as the operator stops to redress the wheel to maintain desired tolerances of the machined surface. The reject rate of such an operation may also be relatively high if the desired tolerances are small and the work pieces are inserted and held at an improper angel. Moreover, this type of operation can be relatively dangerous if, for example, the work piece is relatively small and the operator's fingers must be close to the grinding wheels to hold the work piece in the correct position.
Another prior method of machining such work pieces includes the use of two or more machines that are run by one operator standing between the machines. In this instance, each machine includes a fixture adapted to releasably hold a work piece during the desired machining operation, and the operation of the machines are timed so that one machine is in a "dwell" period while the other machine is cutting a work piece. With this arrangement, the operator removes the finished work piece and installs a fresh work piece for machining into each machine during its respective dwell period by turning back and forth between the machines. Although in some instances, productivity and accuracy of the finished parts may increase with this method when compared with manually holding work pieces in a centerless grinder, such an arrangement is still relatively slow, and the requires the capital expense of two machines.